Endoscopes serve for observing cavities in human or animal bodies and in technical objects, and can have a rigid, semi-rigid or flexible embodiment. A rigid endoscope comprises an elongate endoscope shank which is suitable for insertion into a cavity to be observed, and a head that can have attachments and control elements and also an eyepiece lens. Inside the endoscope shank and the head there is arranged an optical system for transmitting an endoscopic image from the distal end of the endoscope, i.e. the end remote from the observer, to the proximal end, i.e. the end near the observer. For this purpose, the optical system comprises in particular a distally arranged objective for receiving the endoscopic image, an image carrier, and an eyepiece arranged at the proximal end of the endoscope, with an eyepiece lens for viewing the transmitted endoscopic image. The image carrier of a rigid endoscope is generally embodied as a rod lens arrangement with rod lenses arranged along an optical axis and, optionally, with further lenses. Furthermore, the endoscope can comprise illumination optical waveguides for illuminating the cavity to be observed and, optionally, further devices, such as e.g. channels for endoscopic work instruments.
Spacers, which are e.g. embodied as short cylindrical tube pieces and prevent direct contact between neighboring lenses and keep the latter at a distance from one another, are generally arranged between the lenses of the optical system. Conventionally, the rod lenses and the spacers and optional further optical elements of the rod lens arrangement are held in an optics tube of the endoscope and are freely displaceable therein due to an external diameter which is slightly smaller than the internal diameter of the optics tube. In the distal direction, the optical elements are pretensioned against a distal termination of the optics tube, which can e.g. be provided by a cover lens, by a system spring and a system termination guide. As a result of this, the lenses are, in the longitudinal direction, kept at their respective position, predetermined on the basis of the calculation of the optical system, and at a distance from one another by the spacers.
During use, endoscopes are subject to significant mechanical and thermal loads. Thus, during handling, accelerations or tremors or impacts can act on the endoscope, and these can lead to movements and dynamic loads on the lenses and the other optical components. Here, the contact regions between the spacers and the rod lenses are particularly problematic since the force exerted on the optical system by pretension and the dynamic forces generated by tremors or impacts are transmitted in these regions. The spacers generally have an embodiment with relatively thin walls in order to avoid substantial reduction in the clear diameter usable for image transmission; therefore, the contact pressure occurring in these regions is very high, particularly in the case of dynamic loads. This can create abrasion which can lead to the generation of stray light. Furthermore, spalling may occur on the faces of the lenses under load from the spacers, as a result of which the quality of the transmitted endoscopic image can be significantly impaired. This can create significant repair outlay.
In order to reduce the risk of damage to the lenses spaced apart by the spacers by the forces applied to the lenses by the spacers, the utility model specification DE 202 01 890 U1 proposes to design a spacer in respect of form or material composition in such a way that, at the contact faces between the spacer and a lens, said spacer exerts a small notch effect on lenses. To this end, the spacer has a material with a lower surface hardness or an elastic embodiment on the contact faces in order to limit the force exerted on the lens.